Zambia’s climate is characterized by a dry period, which runs from May to October, and a wet period that runs from November to April. Because most of the country’s agriculture is rainfed, rainfall variability poses challenges for food security and planning. Agriculture accounts for about 20 percent of Gross Domestic Product (GDP), with maize as the dominant crop (the other main crops are wheat, sorghum, cassava, rice, millet, groundnuts, soybeans, mixed beans, peanuts, sunflower seed, vegetables, coffee, flowers, tobacco, cotton, and sugarcane). Agricultural jobs account for 71.6 percent of employment in Zambia. During the period between 1960 and 2008, the population increased by more than 50 percent. The urbanization rate in Zambia has averaged 4.3 percent over the past 50 years.